If the lipid in the chyme aggregates into large globules, very little surface area of the lipids is available for the lipases to act on, leaving lipid digestion incomplete. Why is emulsification important for digestion of lipids? Pancreatic juices contain enzymes called lipases (enzymes that break down lipids). By doing so, bile salts emulsify large lipid globules into small lipid globules. Thus, the bile salts hydrophilic side can interface with water on one side and the hydrophobic side interfaces with lipids on the other. Bile contains bile salts, which are amphipathic, meaning they contain hydrophobic and hydrophilic parts. Lipids are hydrophobic substances: in the presence of water, they will aggregate to form globules to minimize exposure to water. These small globules are more widely distributed in the chyme rather than forming large aggregates. ![]() Emulsification is a process in which large lipid globules are broken down into several small lipid globules. Bile aids in the digestion of lipids, primarily triglycerides by emulsification. When chyme enters the duodenum, the hormonal responses trigger the release of bile, which is produced in the liver and stored in the gallbladder. However, the bulk of lipid digestion occurs in the small intestine due to pancreatic lipase. Lipid digestion begins in the stomach with the aid of lingual lipase and gastric lipase. The steps in carbohydrate digestion are summarized in and. The monosaccharides are transported across the intestinal epithelium into the bloodstream to be transported to the different cells in the body. The monosaccharides (glucose) thus produced are absorbed and then can be used in metabolic pathways to harness energy. Sucrase breaks down sucrose (or “table sugar”) into glucose and fructose, and lactase breaks down lactose (or “milk sugar”) into glucose and galactose. Other disaccharides, such as sucrose and lactose are broken down by sucrase and lactase, respectively. Maltase breaks down maltose into glucose. The disaccharides are broken down into monosaccharides by enzymes called maltases, sucrases, and lactases, which are also present in the brush border of the small intestinal wall. ![]() Pancreatic juices also contain amylase, which continues the breakdown of starch and glycogen into maltose, a disaccharide. Recall that the chyme from the stomach enters the duodenum and mixes with the digestive secretion from the pancreas, liver, and gallbladder. The next step of carbohydrate digestion takes place in the duodenum. The acidic environment in the stomach stops the action of the amylase enzyme. The esophagus produces no digestive enzymes but does produce mucous for lubrication. As the bolus of food travels through the esophagus to the stomach, no significant digestion of carbohydrates takes place. The salivary enzyme amylase begins the breakdown of food starches into maltose, a disaccharide. The digestion of carbohydrates begins in the mouth.
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